Islamic extremists overran three towns in northern Syria this weekend, capturing them from Western-backed Free Syrian Army rebels and Islamist brigades as Syrian warplanes struck widely across the north of the country, dropping barrel bombs on towns controlled by both competing insurgent groups.

Despite FSA claims that Syrian President Bashar al-Assad and the Islamic State, also known as ISIL, were coordinating their attacks, two of the biggest barrel bombs were dropped on the town of Al Bab, controlled by Islamic State.

The bombs dropped Saturday on a crowded market in the center of the town northeast of Aleppo left at least 71 people dead, including children, according to local political activists.

Another barrel bomb also was dropped on Aleppo, which is half-controlled by rebels aligned with the FSA killed 21 people.

It was a quick and unexpected offensive north of Aleppo, however, deep into FSA territory by IS that triggered panic among rebel commanders and Islamist allies. The Islamic extremists threatened to do what Assad’s forces have failed to pull off — namely severing the rebels’ crucial supply lines to Turkey.

IS offensives

IS fighters stormed the town of Sawran. And they captured the villages of Umm Hawash and Al-Hasiyah after intense clashes on Sunday morning before launching assaults on the towns of Marea and Azaz, which FSA fighters and Islamist militias managed to repel.

Rebel commanders said they had asked the United States to launch airstrikes on the attacking IS forces to help them to defend Marea and Azaz, which control the roads leading to the Turkish border crossing at Kilis. U.S. officials have been wary of being drawn into the conflict around Aleppo and have been focusing their airstrikes on IS targets in western Iraq and eastern Syria.

Analyst Emile Hokayem of the International Institute for Strategic Studies, a U.K-based think tank, warned Sunday, though, that the moment had come for Gulf Arab members of the U.S.-led anti-IS coalition to help Syrian rebels now by pressuring the United States to conduct strikes north of Aleppo.

By Sunday night, reinforcements from a rebel alliance called Jaish al Fatah [Army of Conquest] in the neighboring province of Idlib to the west of Aleppo, arrived to hold IS from seizing Marea and Azaz. According to analyst Charles Lister of the Brookings Doha Center, a think tank, the fall of Azaz would have “major implications” for the rebels.

Several of the brigades rushing to forestall IS from capturing Azaz included the U.S.-favored Nour al-Din al-Zenki, Division 13 and Fursan Al Haq militias. They were joined by fighters from al-Qaida affiliate Jabhat al-Nusra, a rival of IS. Al Nusra launched a suicide bomb attack Sunday to try to forestall IS.

“The situation is getting a little better in the North after the reinforcements arrived, it is still dangerous but the advancing stopped,” tweeted activist Yusuf Eissa.

He, like many activists and rebels, accused Assad and IS of coordinating the attacks on rebel positions north of Aleppo — a frequent claim by them.

But in the many-sided, long-running conflict in Syria, all sides try to benefit from the complexity of the battlefield and to take advantage of any openings created, even by their foes, to strike at other opponents, say analysts. While fighting raged north of Aleppo at the weekend. Kurdish fighters also opposed to Assad and al Nusra militiamen clashed in the city.

Brutal barrel-bombings

The intensity of the barrel-bombing combined with the IS ground offensive appeared to stretch the rebels to the limits and their commanders were warning Sunday night that the loss of either Azaz or Marea, allowing IS to control access to the border with Turkey,
would be a devastating blow for their cause.

The shifting of reinforcements from Idlib, where the rebels have recently pulled off stunning battlefield successes against Assad’s forces, including severing the main ground supply route from coastal Syria to Aleppo, is likely to have longer-term consequences for the rebels’ future strategy.

Following the military gains in April and May in Idlib province, the Army of Conquest’s commanders have been extremely reluctant to refocus on Aleppo and join rebel militias there. They have been discussing a strike south, toward Hama and then Homs, or at Latakia on the coast.

“It would be a mistake to be drawn back into the fight for Aleppo,” said Abu Jaseem, the commander of a militia called the First Regiment. He has been arguing for an assault on Latakia, populated mostly by members of Assad’s minority Alawi sect, an offshoot of Shiite Islam, saying it would send a symbolic, unsettling message to the regime’s supporters.

Others have been arguing for an assault south, according to commanders interviewed by VOA. Now with IS offensive on towns and villages north of Aleppo, the top rebel alliance, the Army of Conquest, is likely to have to delay any moves south or west and risk being drawn into a quagmire around Aleppo.

While rebel brigades battled to hold the line against IS, the UN Special Envoy for Syria Staffan de Mistura strongly condemned the Syrian government barrel bombing on insurgent-held neighborhoods in Aleppo and on outlying towns and villages.

De Mistura focused his complaint on the dropping of barrel bombs on Sunday on a market in the Al Shaar district of Aleppo and on Al Bab. The UN noted many of the victims were blown to pieces or burnt beyond recognition by the blasts.

The envoy said it was “totally unacceptable that the Syrian air force attacks its own territory in an indiscriminate way, killing its own citizens, as it brutally happened today in Aleppo.”

De Mistura added, “The use of barrel bombs must stop. All evidence shows that the overwhelming majority of the civilian victims in the Syrian conflict have been caused by the use of such indiscriminate aerial weapons.”

Khaled Khoja, the president of the Syrian National Coalition, the main political opposition group to Assad, warned Monday that lack of international intervention in support of the rebels “means relinquishing Syria altogether to become a hotbed for two of the most horrible terrorism forces” — the Assad regime and Islamic State. “Syria is stuck between two savage terrorisms. ISIS is progressing along the eastern region of the country towards…Damascus, Homs and Aleppo, thus putting our people and our rebel fighters between a rock and a hard place while the world watches motionless.”

At a press conference he appealed to neighboring countries “to coordinate amongst themselves in light of the inaction of the international community, and to act as one hand and intervene immediately to prevent their neighbor Syria from turning into a hotbed for the worst kinds of terrorism.”